1. Field of the Invention
The present invention relates to a method and system for detecting echo signals by simultaneous reception in an ultrasound diagnosis apparatus.
2. Description of the Related Art
When linear scanning is to be performed in an ultrasound diagnosis apparatus having an ultrasound probe in which a plurality of transducers are arranged, the transducers are sequentially driven to transmit an ultrasound beam, and an ultrasound beam reflected by an object to be examined is received as an echo signal by the same transducer which is driven to transmit the ultrasound beam. In this case, ultrasound beams reflected by the object to be examined are focused (electron-focused) by shifting drive timings of transducers arranged in a central portion of the ultrasound probe from those of transducers arranged in its end portions.
In order to perform sector scanning, drive timings of the transducers are changed to form a sector transmission area of ultrasound beams, thereby receiving echo signals.
Image display methods are classified into B mode image display for displaying an ultrasound tomographic image obtained by synthesizing echo signals and M mode image display for displaying a time change in ultrasound transmission/reception signals. The M mode is used in diagnosis of an organ which rapidly moves such as a heart. Doppler image display is performed by using an ultrasound Doppler effect in which the frequency of an echo signal from a moving object is shifted in proportion to the speed of the moving object. That is, information of a moving object in a depth position corresponding to the echo signal is obtained by detecting a frequency shift of an echo signal from a living body. Therefore, information of, e.g., a blood flow direction, a blood flow state, a blood flow pattern, and a blood flow rate on a predetermined slice in a living body can be displayed.
A speckled pattern called a speckle appears in a B mode image obtained by an ultrasound diagnosis apparatus. This pattern is produced when ultrasound beams from transducers arranged in an ultrasound probe are incident on small scattered bodies and waves (echo signals) reflected by the small scattered bodies interfere with each other. Therefore, this speckle is caused by coherency of an ultrasound beam.
That is, since phases of ultrasound beams transmitted in a living body coincide with each other, echo signals from a large number of scattering portions present in the living body interfere with each other on the receiving surface of the ultrasound probe. Therefore, fluctuation occurs in an amplitude of the echo signal to produce a speckled pattern, i.e., a speckle on the B mode image, thereby degrading image quality.
As a method of reducing speckle noise, a real-time reducing method for speckle noise in a B mode image is available. For example, a plurality of echo signals are obtained by spatial compound scanning in which transmission/reception is performed with respect to a predetermined observation point in a living body while an ultrasound probe is moved. The obtained echo signals are input to a plurality of filters having different pass bands. Output signals from the filters are subjected to envelope detection and added to each other. Accordingly, a scanning corresponding to frequency compound scanning is performed. After a plurality of echo signals obtained by spatial compound scanning are processed as described above, the processed signals are superimposed with each other. By performing the above processing for a predetermined portion in a living body, an ultrasound image in which a speckle noise is reduced can be obtained in real time by the two compound scanning.
In this method, however, a long time period is required to display an image because echo signals are obtained by moving the ultrasound probe. In addition, since it takes a long time period to obtain echo signals in different directions from an observation point in a living body, this method cannot be applied to a moving object. Furthermore, if a correct position and a correct angle of a moving ultrasound probe cannot be obtained, a positional deviation occurs in an observation point.
For the above reasons, a demand has arisen for an ultrasound diagnosis apparatus which can display an ultrasound image with reduced speckle noise in real time.